C# GetHashCode与Equals在HashTable表查找时的关系

using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Win32;
using System.Threading;
using System.IO;
using System.Security.Cryptography;
using Common;

namespace ConsoleApplication2
{
    public class Test
    {
        private string _id;

        public string Id
        {
            get { return _id; }
            set { _id = value; }
        }

        public Test(string id)
        {
            _id = id;
        }

        public override int GetHashCode()
        {
            Console.WriteLine("GetHashCode()");
            return Id.Length;
        }

        public override bool Equals(object obj)
        {
            Console.WriteLine("Equals()");
            return Id == (obj as Test).Id;
        }
    }

    class Program
    {
        /// <summary>
        /// 如果GetHashCode相等则不用Equals了，否则需要Equals
        /// </summary>
        /// <param name="args"></param>
        static void Main(string[] args)
        {
            Dictionary<Test, string> dc = new Dictionary<Test, string>();

            Test t1 = new Test("a");
            Test t2 = new Test("b");
            Test t3 = new Test("cc"); 

            dc.Add(t1, "");
            Console.WriteLine("----------------");
            Console.WriteLine(dc.ContainsKey(t1));
            Console.WriteLine("----------------");
            Console.WriteLine(dc.ContainsKey(t2));
            Console.WriteLine("----------------");
            Console.WriteLine(dc.ContainsKey(t3));

        }
    }
}